1. Field of the Invention
This invention relates to a pressure source for a pressure device, comprising a pump for pumping a fluid from a fluid tank, an accumulator connected to the pump and to a pressure device, pressure detecting means for detecting the pressure in the accumulator, and a control system for controlling the operation of the pump in an ON/OFF manner on the basis of results of detection of the pressure detecting means.
2. Description of the Prior Art
There is a conventionally known pressure source of the above-described type for a pressure device, used in a brake device, or the like, for a vehicle and which includes, as the pressure detecting means, a pressure switch for detecting the pressure in the accumulator to produce an ON/OFF signal, and a pressure sensor for outputting a pressure signal corresponding to the pressure in the accumulator to detect whether the pressure switch is normal or out of order.
The above-described prior art pressure source for the pressure device is constructed, as shown in FIG. 7, so that if the pressure in the accumulator is reduced, thereby permitting the pressure switch 1 to be turned OFF, the pump is started to increase the pressure in the accumulator, and if the pressure in the accumulator is increased, thereby permitting the pressure switch 1 to be turned ON, the pump is stopped. If the pressure sensor detects the pressure in the accumulator being increased to exceed a judging value F.sub.PH, or being reduced to exceed a judging value F.sub.PL, it is judged that the pressure switch is out of order.
In the above-described prior art pressure source, each of the judging values F.sub.PH and F.sub.PL as a criterion for judgement of the trouble of the pressure switch is a fixed value. For this reason, if the operating pressure for the pressure switch is offset or deflected toward a high pressure side due to a variation that may be generated during manufacturing, as shown by 2 in FIG. 7, it is mis-judged that the pressure switch has an OFF trouble (a trouble of the pressure switch fixed at its OFF position). In contrast, if the operating pressure for the pressure switch is offset or deflected toward a low pressure side as shown by 3, it is mis-judged that the pressure switch has an ON trouble (a trouble of the pressure switch fixed at its ON position).
If the interval between the judging values F.sub.PH and F.sub.PL as criteria for judgement of the troubles is set larger, as shown in FIG. 8, in order to avoid the above-described misjudgement, the range of controlling hydraulic pressure becomes wider, and as a result, an abnormal increase or reduction in hydraulic pressure may be caused.